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/*!
* \file sbas_l1_telemetry_decoder_cc.cc
* \brief Implementation of a SBAS telemetry data decoder block
* \author Daniel Fehr 2013. daniel.co(at)bluewin.ch
*
* -------------------------------------------------------------------------
*
* Copyright (C) 2010-2018 (see AUTHORS file for a list of contributors)
*
* GNSS-SDR is a software defined Global Navigation
* Satellite Systems receiver
*
* This file is part of GNSS-SDR.
*
* GNSS-SDR is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* GNSS-SDR is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with GNSS-SDR. If not, see <https://www.gnu.org/licenses/>.
*
* -------------------------------------------------------------------------
*/
#include "sbas_l1_telemetry_decoder_cc.h"
#include "gnss_synchro.h"
#include <boost/lexical_cast.hpp>
#include <glog/logging.h>
#include <gnuradio/io_signature.h>
#include <sstream>
using google::LogMessage;
// logging levels
#define EVENT 2 // logs important events which don't occur every block
#define FLOW 3 // logs the function calls of block processing functions
#define SAMP_SYNC 4 // about 1 log entry per sample -> high output
#define LMORE 5 //
sbas_l1_telemetry_decoder_cc_sptr
sbas_l1_make_telemetry_decoder_cc(const Gnss_Satellite &satellite, bool dump)
{
return sbas_l1_telemetry_decoder_cc_sptr(new sbas_l1_telemetry_decoder_cc(satellite, dump));
}
sbas_l1_telemetry_decoder_cc::sbas_l1_telemetry_decoder_cc(
const Gnss_Satellite &satellite,
bool dump) : gr::block("sbas_l1_telemetry_decoder_cc",
gr::io_signature::make(1, 1, sizeof(Gnss_Synchro)),
gr::io_signature::make(1, 1, sizeof(Gnss_Synchro)))
{
// Ephemeris data port out
this->message_port_register_out(pmt::mp("telemetry"));
// initialize internal vars
d_dump = dump;
d_satellite = Gnss_Satellite(satellite.get_system(), satellite.get_PRN());
LOG(INFO) << "SBAS L1 TELEMETRY PROCESSING: satellite " << d_satellite;
d_block_size = D_SAMPLES_PER_SYMBOL * D_SYMBOLS_PER_BIT * D_BLOCK_SIZE_IN_BITS;
d_channel = 0;
set_output_multiple(1);
}
sbas_l1_telemetry_decoder_cc::~sbas_l1_telemetry_decoder_cc()
{
if (d_dump_file.is_open() == true)
{
try
{
d_dump_file.close();
}
catch (const std::exception &ex)
{
LOG(WARNING) << "Exception in destructor closing the dump file " << ex.what();
}
}
}
void sbas_l1_telemetry_decoder_cc::set_satellite(const Gnss_Satellite &satellite)
{
d_satellite = Gnss_Satellite(satellite.get_system(), satellite.get_PRN());
LOG(INFO) << "SBAS telemetry decoder in channel " << this->d_channel << " set to satellite " << d_satellite;
}
void sbas_l1_telemetry_decoder_cc::set_channel(int32_t channel)
{
d_channel = channel;
LOG(INFO) << "SBAS channel set to " << channel;
}
// ### helper class for sample alignment ###
sbas_l1_telemetry_decoder_cc::Sample_Aligner::Sample_Aligner()
{
d_n_smpls_in_history = 3;
d_iir_par = 0.05;
reset();
}
sbas_l1_telemetry_decoder_cc::Sample_Aligner::~Sample_Aligner() = default;
void sbas_l1_telemetry_decoder_cc::Sample_Aligner::reset()
{
d_past_sample = 0;
d_corr_paired = 0;
d_corr_shifted = 0;
d_aligned = true;
}
/*
* samples length must be a multiple of two
*/
bool sbas_l1_telemetry_decoder_cc::Sample_Aligner::get_symbols(const std::vector<double> &samples, std::vector<double> &symbols)
{
double smpls[3] = {};
double corr_diff;
bool stand_by = true;
double sym;
VLOG(FLOW) << "get_symbols(): "
<< "d_past_sample=" << d_past_sample << "\tsamples size=" << samples.size();
for (uint32_t i_sym = 0; i_sym < samples.size() / sbas_l1_telemetry_decoder_cc::D_SAMPLES_PER_SYMBOL; i_sym++)
{
// get the next samples
for (int32_t i = 0; i < d_n_smpls_in_history; i++)
{
smpls[i] = static_cast<int32_t>(i_sym) * sbas_l1_telemetry_decoder_cc::D_SAMPLES_PER_SYMBOL + i - 1 == -1 ? d_past_sample : samples[i_sym * sbas_l1_telemetry_decoder_cc::D_SAMPLES_PER_SYMBOL + i - 1];
}
// update the pseudo correlations (IIR method) of the two possible alignments
d_corr_paired = d_iir_par * smpls[1] * smpls[2] + (1 - d_iir_par) * d_corr_paired;
d_corr_shifted = d_iir_par * smpls[0] * smpls[1] + (1 - d_iir_par) * d_corr_shifted;
// decide which alignment is the correct one
corr_diff = std::abs(d_corr_paired - d_corr_shifted);
stand_by = d_aligned ? corr_diff < d_corr_paired / 2 : corr_diff < d_corr_shifted / 2;
if (!stand_by)
{
d_aligned = d_corr_paired >= d_corr_shifted;
}
// sum the correct pair of samples to a symbol, depending on the current alignment d_align
sym = smpls[0 + int32_t(d_aligned) * 2] + smpls[1];
symbols.push_back(sym);
// sample alignment debug output
VLOG(SAMP_SYNC) << std::setprecision(5)
<< "smplp: " << std::setw(6) << smpls[0] << " "
<< "smpl0: " << std::setw(6)
<< smpls[1] << " "
<< "smpl1: " << std::setw(6) << smpls[2] << "\t"
//<< "Flag_valid_tracking: " << std::setw(1) << in[0][0].Flag_valid_tracking << " " << std::setw(1) << in[0][0].Flag_valid_tracking << "\t"
<< "d_corr_paired: " << std::setw(10) << d_corr_paired << "\t"
<< "d_corr_shifted: " << std::setw(10) << d_corr_shifted << "\t"
<< "corr_diff: " << std::setw(10) << corr_diff << "\t"
<< "stand_by: " << std::setw(1) << stand_by << "\t"
<< "d_aligned: " << std::setw(1) << d_aligned << "\t"
<< "sym: " << std::setw(10) << sym << "\t";
}
// save last sample for next block
double temp;
temp = samples.back();
d_past_sample = (temp);
return d_aligned;
}
// ### helper class for symbol alignment and viterbi decoding ###
sbas_l1_telemetry_decoder_cc::Symbol_Aligner_And_Decoder::Symbol_Aligner_And_Decoder()
{
// convolutional code properties
d_KK = 7;
const int32_t nn = 2;
int32_t g_encoder[nn];
g_encoder[0] = 121;
g_encoder[1] = 91;
d_vd1 = new Viterbi_Decoder(g_encoder, d_KK, nn);
d_vd2 = new Viterbi_Decoder(g_encoder, d_KK, nn);
d_past_symbol = 0;
}
sbas_l1_telemetry_decoder_cc::Symbol_Aligner_And_Decoder::~Symbol_Aligner_And_Decoder()
{
delete d_vd1;
delete d_vd2;
}
void sbas_l1_telemetry_decoder_cc::Symbol_Aligner_And_Decoder::reset()
{
d_past_symbol = 0;
d_vd1->reset();
d_vd2->reset();
}
bool sbas_l1_telemetry_decoder_cc::Symbol_Aligner_And_Decoder::get_bits(const std::vector<double> &symbols, std::vector<int32_t> &bits)
{
const int32_t traceback_depth = 5 * d_KK;
int32_t nbits_requested = symbols.size() / D_SYMBOLS_PER_BIT;
int32_t nbits_decoded;
// fill two vectors with the two possible symbol alignments
std::vector<double> symbols_vd1(symbols); // aligned symbol vector -> copy input symbol vector
std::vector<double> symbols_vd2; // shifted symbol vector -> add past sample in front of input vector
symbols_vd2.push_back(d_past_symbol);
for (auto symbol_it = symbols.cbegin(); symbol_it != symbols.cend() - 1; ++symbol_it)
{
symbols_vd2.push_back(*symbol_it);
}
// arrays for decoded bits
auto *bits_vd1 = new int32_t[nbits_requested];
auto *bits_vd2 = new int32_t[nbits_requested];
// decode
float metric_vd1 = d_vd1->decode_continuous(symbols_vd1.data(), traceback_depth, bits_vd1, nbits_requested, nbits_decoded);
float metric_vd2 = d_vd2->decode_continuous(symbols_vd2.data(), traceback_depth, bits_vd2, nbits_requested, nbits_decoded);
// choose the bits with the better metric
for (int32_t i = 0; i < nbits_decoded; i++)
{
if (metric_vd1 > metric_vd2)
{ // symbols aligned
bits.push_back(bits_vd1[i]);
}
else
{ // symbols shifted
bits.push_back(bits_vd2[i]);
}
}
d_past_symbol = symbols.back();
delete[] bits_vd1;
delete[] bits_vd2;
return metric_vd1 > metric_vd2;
}
// ### helper class for detecting the preamble and collect the corresponding message candidates ###
void sbas_l1_telemetry_decoder_cc::Frame_Detector::reset()
{
d_buffer.clear();
}
void sbas_l1_telemetry_decoder_cc::Frame_Detector::get_frame_candidates(const std::vector<int32_t> &bits, std::vector<std::pair<int32_t, std::vector<int32_t>>> &msg_candidates)
{
std::stringstream ss;
uint32_t sbas_msg_length = 250;
std::vector<std::vector<int32_t>> preambles = {{0, 1, 0, 1, 0, 0, 1, 1},
{1, 0, 0, 1, 1, 0, 1, 0},
{1, 1, 0, 0, 0, 1, 1, 0}};
VLOG(FLOW) << "get_frame_candidates(): "
<< "d_buffer.size()=" << d_buffer.size() << "\tbits.size()=" << bits.size();
ss << "copy bits ";
int32_t count = 0;
// copy new bits into the working buffer
for (auto bit_it = bits.cbegin(); bit_it < bits.cend(); ++bit_it)
{
d_buffer.push_back(*bit_it);
ss << *bit_it;
count++;
}
VLOG(SAMP_SYNC) << ss.str() << " into working buffer (" << count << " bits)";
int32_t relative_preamble_start = 0;
while (d_buffer.size() >= sbas_msg_length)
{
// compare with all preambles
for (auto preample_it = preambles.begin(); preample_it < preambles.end(); ++preample_it)
{
bool preamble_detected = true;
bool inv_preamble_detected = true;
// compare the buffer bits with the preamble bits
for (auto preample_bit_it = preample_it->begin(); preample_bit_it < preample_it->end(); ++preample_bit_it)
{
preamble_detected = *preample_bit_it == d_buffer[preample_bit_it - preample_it->begin()] ? preamble_detected : false;
inv_preamble_detected = *preample_bit_it != d_buffer[preample_bit_it - preample_it->begin()] ? inv_preamble_detected : false;
}
if (preamble_detected || inv_preamble_detected)
{
// copy candidate
std::vector<int32_t> candidate;
std::copy(d_buffer.begin(), d_buffer.begin() + sbas_msg_length, std::back_inserter(candidate));
if (inv_preamble_detected)
{
// invert bits
for (int &candidate_bit_it : candidate)
{
candidate_bit_it = candidate_bit_it == 0 ? 1 : 0;
}
}
msg_candidates.emplace_back(relative_preamble_start, candidate);
ss.str("");
ss << "preamble " << preample_it - preambles.begin() << (inv_preamble_detected ? " inverted" : " normal") << " detected! candidate=";
for (auto bit_it = candidate.begin(); bit_it < candidate.end(); ++bit_it)
{
ss << *bit_it;
}
VLOG(EVENT) << ss.str();
}
}
relative_preamble_start++;
// remove bit in front
d_buffer.pop_front();
}
}
// ### helper class for checking the CRC of the message candidates ###
void sbas_l1_telemetry_decoder_cc::Crc_Verifier::reset()
{
}
void sbas_l1_telemetry_decoder_cc::Crc_Verifier::get_valid_frames(const std::vector<msg_candiate_int_t> &msg_candidates, std::vector<msg_candiate_char_t> &valid_msgs)
{
std::stringstream ss;
VLOG(FLOW) << "get_valid_frames(): "
<< "msg_candidates.size()=" << msg_candidates.size();
// for each candidate
for (auto candidate_it = msg_candidates.cbegin(); candidate_it < msg_candidates.cend(); ++candidate_it)
{
// convert to bytes
std::vector<uint8_t> candidate_bytes;
zerropad_back_and_convert_to_bytes(candidate_it->second, candidate_bytes);
// verify CRC
d_checksum_agent.reset(0);
d_checksum_agent.process_bytes(candidate_bytes.data(), candidate_bytes.size());
uint32_t crc = d_checksum_agent.checksum();
VLOG(SAMP_SYNC) << "candidate " << candidate_it - msg_candidates.begin()
<< ": final crc remainder= " << std::hex << crc
<< std::setfill(' ') << std::resetiosflags(std::ios::hex);
// the final remainder must be zero for a valid message, because the CRC is done over the received CRC value
if (crc == 0)
{
valid_msgs.emplace_back(candidate_it->first, candidate_bytes);
ss << "Valid message found!";
}
else
{
ss << "Not a valid message.";
}
ss << " Relbitoffset=" << candidate_it->first << " content=";
for (auto byte_it = candidate_bytes.begin(); byte_it < candidate_bytes.end(); ++byte_it)
{
ss << std::setw(2) << std::setfill('0') << std::hex << static_cast<uint32_t>((*byte_it));
}
VLOG(SAMP_SYNC) << ss.str() << std::setfill(' ') << std::resetiosflags(std::ios::hex) << std::endl;
}
}
void sbas_l1_telemetry_decoder_cc::Crc_Verifier::zerropad_back_and_convert_to_bytes(const std::vector<int> &msg_candidate, std::vector<uint8_t> &bytes)
{
std::stringstream ss;
const size_t bits_per_byte = 8;
uint8_t byte = 0;
VLOG(LMORE) << "zerropad_back_and_convert_to_bytes():" << byte;
for (auto candidate_bit_it = msg_candidate.cbegin(); candidate_bit_it < msg_candidate.cend(); ++candidate_bit_it)
{
int32_t idx_bit = candidate_bit_it - msg_candidate.begin();
int32_t bit_pos_in_current_byte = (bits_per_byte - 1) - (idx_bit % bits_per_byte);
byte |= static_cast<uint8_t>(*candidate_bit_it) << bit_pos_in_current_byte;
ss << *candidate_bit_it;
if (idx_bit % bits_per_byte == bits_per_byte - 1)
{
bytes.push_back(byte);
VLOG(LMORE) << ss.str() << " -> byte=" << std::setw(2) << std::setfill('0') << std::hex << static_cast<uint32_t>(byte);
ss.str("");
byte = 0;
}
}
bytes.push_back(byte); // implies: insert 6 zeros at the end to fit the 250bits into a multiple of bytes
VLOG(LMORE) << " -> byte=" << std::setw(2)
<< std::setfill('0') << std::hex << static_cast<uint32_t>(byte)
<< std::setfill(' ') << std::resetiosflags(std::ios::hex);
}
void sbas_l1_telemetry_decoder_cc::Crc_Verifier::zerropad_front_and_convert_to_bytes(const std::vector<int32_t> &msg_candidate, std::vector<uint8_t> &bytes)
{
std::stringstream ss;
const size_t bits_per_byte = 8;
uint8_t byte = 0;
int32_t idx_bit = 6; // insert 6 zeros at the front to fit the 250bits into a multiple of bytes
VLOG(LMORE) << "zerropad_front_and_convert_to_bytes():" << byte;
for (auto candidate_bit_it = msg_candidate.cbegin(); candidate_bit_it < msg_candidate.cend(); ++candidate_bit_it)
{
int32_t bit_pos_in_current_byte = (bits_per_byte - 1) - (idx_bit % bits_per_byte);
byte |= static_cast<uint8_t>(*candidate_bit_it) << bit_pos_in_current_byte;
ss << *candidate_bit_it;
if (idx_bit % bits_per_byte == bits_per_byte - 1)
{
bytes.push_back(byte);
VLOG(LMORE) << ss.str() << " -> byte=" << std::setw(2)
<< std::setfill('0') << std::hex << static_cast<uint32_t>(byte);
ss.str("");
byte = 0;
}
idx_bit++;
}
VLOG(LMORE) << " -> byte=" << std::setw(2)
<< std::setfill('0') << std::hex << static_cast<uint32_t>(byte)
<< std::setfill(' ') << std::resetiosflags(std::ios::hex);
}
int sbas_l1_telemetry_decoder_cc::general_work(int noutput_items __attribute__((unused)), gr_vector_int &ninput_items __attribute__((unused)),
gr_vector_const_void_star &input_items, gr_vector_void_star &output_items)
{
VLOG(FLOW) << "general_work(): "
<< "noutput_items=" << noutput_items << "\toutput_items real size=" << output_items.size() << "\tninput_items size=" << ninput_items.size() << "\tinput_items real size=" << input_items.size() << "\tninput_items[0]=" << ninput_items[0];
// get pointers on in- and output gnss-synchro objects
auto *out = reinterpret_cast<Gnss_Synchro *>(output_items[0]); // Get the output buffer pointer
const auto *in = reinterpret_cast<const Gnss_Synchro *>(input_items[0]); // Get the input buffer pointer
Gnss_Synchro current_symbol{}; // structure to save the synchronization information and send the output object to the next block
// 1. Copy the current tracking output
current_symbol = in[0];
// copy correlation samples into samples vector
d_sample_buf.push_back(current_symbol.Prompt_I); //add new symbol to the symbol queue
// store the time stamp of the first sample in the processed sample block
double sample_stamp = static_cast<double>(in[0].Tracking_sample_counter) / static_cast<double>(in[0].fs);
// decode only if enough samples in buffer
if (d_sample_buf.size() >= d_block_size)
{
// align correlation samples in pairs
// and obtain the symbols by summing the paired correlation samples
std::vector<double> symbols;
bool sample_alignment = d_sample_aligner.get_symbols(d_sample_buf, symbols);
// align symbols in pairs
// and obtain the bits by decoding the symbol pairs
std::vector<int32_t> bits;
bool symbol_alignment = d_symbol_aligner_and_decoder.get_bits(symbols, bits);
// search for preambles
// and extract the corresponding message candidates
std::vector<msg_candiate_int_t> msg_candidates;
d_frame_detector.get_frame_candidates(bits, msg_candidates);
// verify checksum
// and return the valid messages
std::vector<msg_candiate_char_t> valid_msgs;
d_crc_verifier.get_valid_frames(msg_candidates, valid_msgs);
// compute message sample stamp
// and fill messages in SBAS raw message objects
//std::vector<Sbas_Raw_Msg> sbas_raw_msgs;
for (const auto &valid_msg : valid_msgs)
{
int32_t message_sample_offset =
(sample_alignment ? 0 : -1) + D_SAMPLES_PER_SYMBOL * (symbol_alignment ? -1 : 0) + D_SAMPLES_PER_SYMBOL * D_SYMBOLS_PER_BIT * valid_msg.first;
double message_sample_stamp = sample_stamp + static_cast<double>(message_sample_offset) / 1000.0;
VLOG(EVENT) << "message_sample_stamp=" << message_sample_stamp
<< " (sample_stamp=" << sample_stamp
<< " sample_alignment=" << sample_alignment
<< " symbol_alignment=" << symbol_alignment
<< " relative_preamble_start=" << valid_msg.first
<< " message_sample_offset=" << message_sample_offset
<< ")";
//Sbas_Raw_Msg sbas_raw_msg(message_sample_stamp, this->d_satellite.get_PRN(), it->second);
//sbas_raw_msgs.push_back(sbas_raw_msg);
}
// parse messages
// and send them to the SBAS raw message queue
//for(std::vector<Sbas_Raw_Msg>::iterator it = sbas_raw_msgs.begin(); it != sbas_raw_msgs.end(); it++)
// {
//std::cout << "SBAS message type " << it->get_msg_type() << " from PRN" << it->get_prn() << " received" << std::endl;
//sbas_telemetry_data.update(*it);
// }
// clear all processed samples in the input buffer
d_sample_buf.clear();
}
// UPDATE GNSS SYNCHRO DATA
// actually the SBAS telemetry decoder doesn't support ranging
current_symbol.Flag_valid_word = false; // indicate to observable block that this synchro object isn't valid for pseudorange computation
out[0] = current_symbol;
consume_each(1); // tell scheduler input items consumed
return 1; // tell scheduler output items produced
}
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